Mason Murphy: Dispersal congruency and population structure within an imperiled host-parasite system

As a part of my thesis work, I am studying the population structure and gene flow of the salamander mussel (Simpsonaias ambigua), a regionally protected freshwater mussel species distributed throughout eastern North America using a genome-wide approach. I am comparing these measures of population connectivity to a number of environmental factors in an effort to understand the role of water chemistry and stream bed disturbance on mussel dispersal. While a study of mussel population structure and gene flow in relation to environmental factors alone is useful, gene flow among freshwater mussel populations may also be influenced by additional variables requiring further investigation. Freshwater mussels exhibit a distinctive life cycle, in which they are parasitic for their juvenile life stage, but fully independent as adults. The sessile adults rely on a unique method of dispersal: injecting fish (and other taxa) with glochidia (larvae), which live on gill tissue parasitically until they are large enough to survive in the substrate of river beds. Thus, most freshwater mussels rely on the dispersal capabilities of their hosts for their own dispersal. Simpsonaias ambigua is unique among freshwater mussels in that it is the only mussel species that uses an amphibian host, the mudpuppy (Necturus maculosus), for dispersal (Fig 1). Necturus maculosus is a widespread, fully-aquatic salamander native to eastern North America with a range that encompasses that of S. ambigua. While the relationship between host and mussel warrants further study, until recently the lack of genetic markers for N. maculosus has made examining any population genetic measure in that species difficult. However, I have recently been in contact with C. W. Kilpatrick, the Howard Professor of Zoology and Natural History at the University of Vermont, who has just developed 24 microsatellite markers for Necturus maculosus. These new markers can allow for an in-depth study on the population genetics and dispersal of N. maculosus, benefiting not only the understanding of population connectivity among N. maculosus populations, but allow for a comparative analysis of dispersal congruency between host salamander and mussel. Using these new tools, we propose to examine the relationship between host and mussel dispersal, gene flow, and population structure. We will generate microsatellite genetic data (24 loci) from Necturus populations that are co-distributed with S. ambigua populations currently under study and we will combine the results generated from our mussel population genomic data with population genetic results generated from the salamander host to test hypotheses about taxon-specific population histories, and hypotheses concerning the shared population history of these two species. Overall, understanding the complex relationship between parasite and host dispersal within a dendritic network will not only offer insight into basic processes of dispersal, gene flow, and potential barriers, but can also shed light on fundamental co-evolutionary processes between two functionally linked organisms.